There has been a power amplifying apparatus which includes a high-frequency amplifying means including transistors arranged in a plurality of stages and a feed-forwarding means which includes a detector that extracts a part of a high-frequency signal from an input side of the high-frequency amplifying means and transfers the extracted signal to an envelopes signal. The feed-forwarding means injects low-frequency signal output from the detector to a gate or a base-bias of the final stage of the high-frequency amplifying means (see, for example, patent document 1).
According to the conventional power amplifying apparatus, the feed-forwarding means injects the low-frequency signal output from the detector to the gate or the base-bias of the final stage of the high-frequency amplifying means.
However, an amplifying part of the final stage has larger size and greater gate capacitance than those of a primary stage. Therefore, it may be difficult to cause an output signal of the final stage to track an input signal of the high-frequency amplifying means, even though the feed-forwarding means injects the low-frequency signal output from the detector to the gate or the base-bias of the final stage.
In a case where it is difficult to cause the output signal of the final stage to track the input signal of the high-frequency amplifying means, the output signal may be distorted. If the output signal of the final stage is distorted, output signal-gain characteristics of the power amplifying apparatus become non-constant. Particularly, the distortion of the output signal becomes remarkable as a power of the output signal becomes higher.